Zinc dialkyl dithiophosphates



United States Patent O ZINC DIALKYL DETHIQPHOSPHATES Richard F. Reeves, Somervilie, and Dominic J. Cestoni, Metedeconk, N. J., assignors to American Cyanamid Company, New York, N. 1., a corporation of Maine N Drawing. Application May 12, 1955 Serial No. 507,984

9 Claims. (Cl. 260-4293) This invention relates to methods of preparing improvement agents for lubricants and more particularly relates to methods of preparing mineral lubricating oil improvement agents comprising metallic salts of dialkyl dithiophosphon'c acid having increased resistance to the formation of haze, greater compatibility with other improvement agents, notatably basic barium petroleum sulfonates, and improved odor characteristics, notably due to the absence of hydrogen sulfide gases.

Oil-soluble metallic salts of dialkyl dithiophosphoric acid, notably zinc dialkyl dithiophosphate, have been employed as improvement agents for lubricants and have been found to produce high film strength, good oiliness characteristics and excellent resistance to oxidation and corrosion in the lubricants so treated. More specific details on the manufacture and use of these oil additives may be found in the Freuler Patents 2,364,283 and 2,364,284 issued December 5, 1944.

It has been found, however, that, in some cases, disagreeable-smelling gases (notably hydrogen sulfide) have evolved on compounding the dialkyl dithiophosphate salts with lubricating oils whereby the product has been rendered less saleable. Additionally, in other cases, the dialkyl dithiophosphate salts have lacked compatibility when used in conjunction with certain other additives, notably metallic salts of petroleum sulfonic acids, and that haze has developed in the compounded lubricating oil composition.

It is, therefore, a principal purpose of the present invention to provide improved methods of preparation of dialkyl dithiophosphate salts which will not evolve objectionable or disagreeable-smelling gases on compounding with lubricants and which will process greater compatibility for compounding with other additives.

It 'has been found that if phosphorus pentasulfide is reacted in proportions now used in the art with a desired higher aliphatic monohydric alcohol having from 6 to 18 carbon atoms, a reaction product is formed which, if treated with a lower aliphatic monohydric alcohol having from 1 to 4 carbon atoms, will then exhibit the desired hazeand odor-free characteristics and properties described hereinbefore.

The higher aliphatic monohydn'c alcohol having from 6 to 18 carbon atoms may be selected from known alcohols and may contain straight-chain or branched-chain alkyl radicals such as derived from 4-methyl-2-pentanol (methylisobutylcarbinol), hexanol, heptanol, isoheptanol, S-ethyl hexanol, octanol, isooctanol, dodecanol, hexadecanol, octadecanol, etc.

The lower aliphatic monohydric alcohols used in the application of the present invention contain up to four carbon atoms and may be selected from the group com prising methanol, .ethanol, propanol, isopropanol, butanol, etc. The amount of the lower alkanol employed may vary from about to about 25% of the weight of the higher alkanol originally reacted with the phosphorus pentasulfide.

. formula:

E W grams sampleXlOOO co.NaOH normality After the lower alkanol is added to the sulfide-higher alcohol reaction product, a temperature of from about 170 F. to about 200 F. is maintained for from about a half hour to about two and a half hours which conditions will vary depending primarily on the alkanols used. The reaction mixture is then neutralized by adding up to 150% of the theoretical excess of a basic zinc compound such as zinc oxide or zinc hydroxide, until a hydrogen sulfide test is negative.

The neutralized product is then aged at a temperature of from about 140 F. to about 195 F. for from about one half to six hours, depending on the alkanols used or if any blending oil and/or water was added during or before the neutralization procedures.

The neutralized, aged product may then be blended with other additives, such as silicone-oil anti-foam agents, detergents such as sodium-or barium petroleum sulfonate, etc., dropped to a still, stripped and then filtered.

Blending oil may be added before or during the neutralization or after the stripping or filtering to bring the concentration of the additive to desired ranges.

The invention will be further illustrated in more specific detail by the following examples. It should be understood, however, that although these examples may describe in more particular detail some of the very specific features of the invention, they are given primarily for purposes of illustration and the invention in its broader aspects is not to be construed as limitedthereto.

In the following examples, references will be made to a haze test and a hydrogen sulfide test. The haze test is carried out as follows: 10 ml. of the sample, 20 ml. of a basic barium petroleum sulfonate and ml. ofnaphtha are stirred together at room temperature until homogeneous and transferred to a Goetz phosphorus tube. The tube is supported in a vertical position in a rigid support free from vibration and in ordinary interior lightfor 24 hours. Rough handling is avoided and the tube is not exposed to direct sunlight or to complete darkness. At the end of 24 hours the volume of the precipitate in the bottom of the tube is read to the nearest 0.01 ml.

The hydrogen sulfide test is carried out as follows: 20 grams of the sample is mixed thoroughly with 380g. of a hydrogen sulfide-free base blending oil and placed in a 500 ml. narrow-mouth reagent bottle. The bottle is stoppered with a suitable cork wrapped in aluminum foil and then placed in a water bath maintained at a temperature of approximately F. for 1 hour. The bottle is then removed and uncorked and a suitable piece of filter paper which has been previously dipped in sat urated lead acetate solution is quickly placed over the opening of the bottle with a light flat cover over it. After five minutes, the filter paperis removed and examined for any discoloration which would represent a positive hydrogen sulfide test.

Example I Example 5 2200 lbs. (327 gals.) 'of methyl isobutyl carbinol was charged to a reaction vessel and heated with agitation to a temperature of about 155-160 F. 1100 lbs. of phosphorus pentasulfide (powdered, 20 mesh) was added rapidly with good agitation, keeping the temperature below about 195 F. (Temperature here was mar-ntained at about 185 F.) The reaction mixture was held at about 190-195 F. for a half hour after all the phosphorus pentasulfide had been added. A cooled sample was tested and indicated an equivalent weight of approximately 325. This acid batch was then permitted to settle and cool to about 110130 F.

300 lbs. of n-butanol was then charged to a neutralization tank and the cooled acid batc'h was rapidly added thereto through a filter with good agitation, keeping the temperature at about 190-195 F. for about one hour. The n-butanol and acid batch mixture was cooled to about 100 F. and 100 lbs. of water at room temperature was added. 535 lbs. of powdered zinc oxide was then charged to the neutralization tank with agitation, keeping the temperature below about 140 F. A test for hydrogen sulfide at this time showed negative.

The reaction mixture was then aged by heating at a temperature of about 140 F. for a period of about one half hour. After the aging, additional materials such as anti-foam agents, detergents such as sodium petroleum sulfonate, etc., may be added with agitation.

The entire batch was then dropped to a still and stripped at about 29" vacuum and about 185195 F. for about an hour. After the condensate has stopped coming over, a base oil may be added to bring the concentration of additive to any desired value. A filter aid may then be added and the entire batch filtered into a holding tank.

A sample of the product was tested for haze and compatibility and found satisfactory.

Example 6 2200 lbs. (327 gals.) of methyl isobutyl carbinol was charged to a reaction vessel and heated with agitation to a temperature of about 155160 F. 1100 lbs. of phosphorus pentasulfide (powdered, 20 mesh) was added rapidly with good agitation, keeping the temperature below about 195 F. (Temperature here was maintained at about 185 F.) The reaction mixture was held at about 190-195 F. for a half hour after all the phosphorus pentasulfide had been added. A cooled sample was tested and indicated an equivalent weight of approximately 324. This acid batch was then permitted to settle and cool to about 110130 F.

300 lbs. of n-butanol was then charged to a neutralization tank and the cooled acid batch was rapidly added thereto through a filter with good agitation, keeping the temperature at about 187-192" F. for about 1% hours. The n-butanol and acid batch mixture was cooled to about 100 F. and 530 lbs. of powdered zinc oxide was then charged with agitation, keeping the temperature below about 175 F. A test for hydrogen sulfide at this time showed negative.

The reaction mixture was then aged by heating at a temperature of about 170-180 F. for a period of about one-half hour. After the aging, additional materials such as anti-foam agents, detergents such as sodium petroleum sulfonate, etc., may be added with agitation.

The entire batch was then dropped to a still and stripped at about 29" vacuum and about 185-195 F. for about an hour. After the condensate has stopped coming over, a base oil may be added to bring the concentration of additive to any desired value. A filter aid may then be added and the entire batch filtered into a holding tank.

A sample of the product passed the haze and compatibility tests satisfactorily.

p a temperature of about 160 F.

Example 7 2200 lbs. (327 gals.) of methyl isobutyl carbinol was charged to a reaction vessel and heated with agitation to 1100 lbs. of phosphorus pentasulfide (powdered, 20 mesh) was added rapidly with good agitation, keeping the temperature below about 195 F. (Temperature here was maintained at about F.) The reaction mixture washeld at about 193198 F. for a half hour after all the phosphorus pentasulfide had been added. A cooled sample was tested and indicated an equivalent weight of approximately 326. This acid batch was then permitted to settle and cool to about 110-130 F.

300.1bs. of n-butanol was then charged to a neutralization tank and the cooled acid batch was rapidly added thereto through a filter withgood agitation, keeping the temperature at about -19S F. for about one hour. The n-butanol and acid batch mixture was cooled to about 100 F. and 100 lbs. of water at room temperature was added. 570 lbs. of powdered zinc oxide was then charged to the neutralization tank with agitation, keeping the temperature below about 175 F. A test for hydrogen sulfide at this time showed negative.

The reaction mixture was then aged by heating at a temperature of about 175-185 F. for a period of about one-half hour. After the aging, additional materials such as anti-foam agents, detergents such as sodium petroleum sulfonate, etc., may be added with agitation.

The entire batch was then dropped to a still and stripped at about 29" vacuum and about 185-195 F. for about an hour. After the condensate has stopped coming over, a base oil may be added to bring the conccentration of additive to any desired value. A filter aid may then be added and the entire batch filtered into a holding tank.

No precipitate or sediment was observed when a sample of the product was tested in the haze test; no hydrogen sulfide vapors were given off in the hydrogen sulfide test and the lead acetate test paper was not dis-,

colored.

Although we have described specific examples of our inventive concept, we consider the broad aspects of the same not to be limited to the specific substances mentioned therein but to include various other compounds of equivalent function and constitution as set forth in the claims appended hereto. It suitable changes, modifications made without departing from the invention.

What we claim is:

.1. A method of preparing an improvement agent for lubricants comprising the steps of reacting phosphorus pentasulfide with an alcohol having the formula ROH wherein R is a higher alkyl radical having from 6 to 18 carbon atoms to form a reaction product contain ing a dialkyl dithiophosphoric acid, treating the reaction product with an alcohol having the formula R'OH wherein R is a lower alkyl radical having up to 4 carbon atoms at a temperature of from about 170 to about 195 F. for from about A to about 2 /2 hours, neutralizing with a basic zinc compound to form a reaction product containing a zinc dialkyl dithiophosphate and aging said reaction product at a temperature of from about 140 to about 195 F. for from about /2 to about 6 hours.

2. A method as defined in claim 1 wherein the higher alkyl radical is 4-methyl-2-pentyl.

3. A method as defined in claim 1 wherein the lower alkyl radical is n-butyl.

4. A method as defined in claim 1 wherein the lower alkyl radical is isopropyl.

5. A method as defined in alkyl radical is ethyl.

and variations may be the spirit and scope of is understood that any claim 1 wherein the lower for lubricants comprising the steps of reacting phosphorus pentasulfide with 4-methyl-2-pentano1 to form a reaction product containing di(4-methy1-2-pentyl) dithiophosphoric acid, treating the reaction product with n-butanol at a temperature of from about 190 to about 197 F. for from about A: to about 1 /2 hours, neutralizing with zinc oxide to form a reaction product containing zinc di(4-methy1-2-pentyl) dithiophosphate and aging said reaction product at a temperature of from about 140 to about 185 F. for from about /2 to about 3% hours.

7. A method of preparing an improvement agent for lubricants comprising the steps. of reacting phosphorus pentasulfide with 4-methy1-2-pentano1 to form a reaction product containing di(4-methyl-2-pentyl) dithiophosporic acid, treating the reaction product with nbutanol at a temperature of from about 190 to about 197 F. for from about V2 to about 1 /2 hours, neutralizing with zinc oxide to form a reaction product contain ing zinc di(4-methyl-2-penty1) dithiophosphate and aging said reaction product at a temperature of from about 170 to about 185 F. for from about /2 to about 3 /2 hours.

8. A method of preparing an improvement agent for lubricants comprising the steps of reacting phosphorus pentasulfide with 4-methy1-2-pentanol to form a reaction product containing di(4-methyi-2-pentyl) dithi'ophosphoric acid, treating the reaction product with isopropanol at a temperature of from about 185 to about 195 F. for from about /2 to about 2 hours, neutralizing with zinc oxide to form a reaction product containing zinc di(4-methy1-2-pentyi) dithiophosphate and aging said reaction product at a temperature of from about 170 to about 185 F. for from about 1 to about 4 hours.

9. A method of preparing an improvement agent for lubricants comprising the steps of reacting phosphorus pentasulfide with 4-methy1-2-pentanol to form a reaction'product containing a di(4-methy1-2-pentyl) dithiophosphoric acid, treating the reaction product with ethanol at a temperature of from about 160 to about 175 F. for from about 1 to about 3 hours, neutralizing with zinc oxide to form a reaction product containing Zinc di(4-methyl-2-penty1) dithiophosphate and aging said reaction product at a temperature of from about 170 to about 195 F. for from about 1 to about 6 hours.

References Cited in the file of this patent UNITED STATES PATENTS 2,344,393 Cook et a1. Mar. 14, 1944 2,358,305 Cook et a1. Sept. 19, 1944 2,368,000 Cook et a1. Jan. 23, 1945 2,466,408 Funk Apr. 5, 1949 2,689,220 Mulvaney Sept. 14, 1954 

1. A METHOD OF PREPARING AN IMPROVEMENT AGENT FOR LUBRICANTS COMPRISING THE STEPS OF REACTING PHOSPHORUS PENTASULFIDE WITH AN ALCOHOL HAVING THE FORMULA ROH WHEREIN R IS A HIGHER ALKYL RADICAL HAVING FROM 6 TO 18 CARBON ATOMS TO FORM A REACTION PRODUCT CONTAINING A DIALKYL DITHIOPHOSPHORIC ACID, TREAING THE REACTION PRODUCT WITH AN ALCOHOL HVING THE FORMULA R''OH WHEREIN R'' IS A LOWER ALKYL RADICAL HAVING UP TO 4 CARBON ATOMS AT A TEMPERATURE OF FROM ABOUT 170 TO ABOUT 195*F. FOR FROM ABOUT 1/2 TO ABOUT 21/2 HOURS, NEUTRALIZING WITH A BASIC ZINC COMPOUND TO FORM A REACTION PRODUCT CONTAINING A ZINC DIALKYL DITHIOPHOSPHATE AND AGING SAID REACTION PRODUCT AT A TEMPERATURE OF FROM ABOUT 140 TO ABOUT 195*F. FOR FROM ABOUT 1/2 TO ABOUT 6 HOURS. 